There are a number of ways you can push messages to your device:
-> Polling - The mobile application would periodically poll one of your services and check for messages. However, as numerous people have pointed out, notifications are no good if they’re delayed due to a low polling period but the more frequently you poll, the more the battery is going to die.
-> SMS - Android can intercept SMS messages but you are limited by the size of the SMS payload.
-> Open a persistent connection - This fixes the polling issue listed above but would kill the battery.
Now, the leading push notification framework for Android seems to be Android Cloud to Device Messaging Framework (
http://code.google.com/android/c2dm/#push) but it is in beta and you have to apply.
Another option is MQTT (IBM), a real good overview can be found here (
http://tokudu.com/2010/how-to-implement-push-notifications-for-android).
Perry Hoekstra